Method and device for regulating the thickness of rolled products

ABSTRACT

A method of regulating the thickness of a product such as a metal strip processed in a rolling-mill, which mill comprises a position corrected under-load clamping system. The method being characterized in that the rolling mill, within a certain range of positions, is rendered elastic by causing the rolling effort to be responsive to a given preset reference value, and outside said range, the rolling mill recovers at least its natural rigidity or, better still, is made rigid, by properly monitoring said reference value of said effort responsiveness.

United States Patent [191 Mornas Dec. 16, 1975 [541' METHOD AND DEVICEFOR REGULATING 3,527,074 9/1970 Guillot 72/8 THE THICKNESS 0F ROLLEDPRODUCTS 1538117 11/1970 72/8 3,543,549 12/1970 72/8 [75] Inventor: JeanPhilippe Mornas, St. Etienne, 3 55Q413 13/1970 73 France 3,580,0225/1971 Waltz 72/8 [73] Assignee: Compagnie des Ateliers et Forges de laL i S Chamond, Firminy9 St Primary E.\-aminer-Milton S. Mehr E i J bJ-ilt Paris, Attorney, Agent, or Firm-Wenderoth, Lind & Ponack France [22]Filedz. Oct. 27, 1970 [5 ABSTRACT [21] App]. No; 84,299 A method ofregulating the thickness of a product such as a metal strip processed ina rolling-mill, which 30 mill comprises a position corrected under-loadclamp- 1 Forelg Appllcanon Pnomy Data ing system. The method beingcharacterized in that Oct. 31. 1969 ran 69-37440 the rolling mill,within a certain range of positions, is

rendered elastic by causing the rolling effort to be re- [52] U.S. u72/19 pongive to a given preset reference value and utside [5 i] Cl.B2113 said range the rolling recovers at least its natural Fleld 0fSearch l9, or better tu] is made rigid by propgrly monitoring saidreference value of said effort responsive- [56] References Cited ness,

UNITED STATES PATENTS 7 Claims, 1 Drawing Figure 3,416,341 12/1968 Deyet al. 72/8 24 r16 va ider-6n) 20 f- "'1 2 26 I9 23 U.S. Patant Dec. 16,1975 3,926,024

- JEAN PHILIPPE MORNAS,

Inventor Attorneys METHOD AND DEVICE FOR REGULATING THE THICKNESS OFROLLED PRODUCTS This invention relates in general to the continuousregulation of rolled products during the processing thereof, and hasparticular reference to methods and means for regulating the thicknessof a product processed in a rolling mill.

It is known that the thickness of a rolling-mill product, for example ametal strip varies considerably due to the influence exerted by variousparameters which do not remain strictly constant during the entirerolling operation, or even during a single pass. These parameters arerelated:

either to the product itself, such as resistance to distortion,conditions prevailing during the distortion (mainly the lubricationbetween the strip surface and the rolls), thickness and width of themill inlet,

or to the rolling-mill proper of which the opening varies on the onehand on account of its elastic distortion (yield), on the other hand onaccount of various defects such as the eccentricity of the rolls(out-of-true), or also of the irregular play in the oil-film bearings.

Regulation methods are already known for correcting the defects of oneor the other types set forth hereinabove, but these methods areobjectionable in that the adjustments thus accomplished cancel oneanother; in other words, if the defects due to the irregular propertiesof the incoming products are corrected, those resulting fromrolling-mill defects are increased, and vice-versa.

It is the essential object of the present invention to provide a methodcapable of overcoming this difficulty by correcting both the defects dueto irregularities in the product to be rolled and the defects due torollingmill defects, mainly its out-of-true or out-of-round.

To this end, the present invention consists essentially of a method ofcontinuously regulating, adjusting and readjusting the thickness of aproduct processed in a rolling mill, equipped with a position-correctedunderload clamping system. According to this method, the rolling mill,within a certain range of positions, is rendered elastic by causing therolling effort to be responsive to a given preset reference value, andoutside said range, the rolling mill recovers at least its naturalrigidity or, better still, is made rigid, by properly monitoring saidreference value of the effort responsiveness.

This invention is also concerned with a regulating device for carryingout the method set forth hereinabove, this device being characterized inthat it comprises:

a. a primary correcting circuit adapted to set the value of the clampingposition correction in such a manner that the measured rolling effort beconstantly very substantially equal to a reference magnitude called theeffort reference value;

b. a secondary correcting circuit adapted to determine the magnitude ofthe effort reference value, this chain comprising;

a dead zone device having the property of transmitting in magnitude andsign of the signal applied to the input of this device, only thefraction lying outside a predetermined range, the limits of this rangebeing disposed symmetrically on either side of a predetermined magnitudecalled a position reference,

a device having integrating and memory functions, which is responsive tosaid dead zone device in such a manner that its output signal is theintegral of the signal delivered by said dead zone device, this outputsignal constituting the effort reference and being fed as such to thereference inlet of said primary circuit;

c. means for displaying the position reference, adjusting the width ofthe dead zone and putting the regulating system into its operative andinoperative conditions, as required.

The invention will now be described in detail with reference to atypical embodiment thereof in the case of a strip rolling mill equippedwith hydraulic means for clamping the product under load. Of course,this example should not be construed as limiting the scope of theinvention.

In the following description reference will be made to the attacheddrawing of which the single FIGURE illustrates the wiring diagram of theregulating device of this invention, associated with the strip rollingmill.

In the drawing, a roll stand 1 is equipped with a hydraulic device 2 forclamping the product being processes under load. In this example thishydraulic device comprises, as shown diagrammatically: a main hydrauliccylinder and piston unit 2 disposed between the lower plummer-block andthe stand bottom; a plunger rod 5 actuated by a control cylinder andpiston unit 3, said rod penetrating into the chamber of the first unit 2and being responsive to a servo-valve 4. Any movement of plunger 5 isaccurately reproduced, except for a dividing factor, by the piston 6 ofthe main hydraulic unit, so as to change the clamping action exerted bythe mill 1.

The main hydraulic unit further comprises a pressure detector 7 formeasuring the effort (rolling effort) exerted by the rolling mill on theproduct. Finally, the position of plunger 5 is also measured by adisplacement detector 8 displaying the degree of clamping movementperformed by the device.

A comparator 27 is provided for comparing this clamping-movement measurewith a reference signal e3 transmitted by wire 9. The resultant signalactuates a corrector amplifier 10 so that the position of plunger 5 andtherefore the clamping effort produced by the clamping device proper isproportional to said reference signal e3.

The use of this hydroelectric device for regulating the clamping forceis described herein only because its very valuable properties, i.e., itsrapidity, precision and reliability, make the device highly adaptable tofeatures characterizing the device of the present invention to bedescribed hereafter. However, it should be emphasized that this choicedoes not constitute a limiting factor as far as the present invention isconcerned, since the invention relates more particularly to the methodof determining the reference signal e3.

This reference signal e3 is produced by an effort regulating circuitcausing the rolling effort (measured by detector 7) to be constantlyresponsive to a reference value ef in wire 11.

To this end, the information received from detector 7 can be added at 12to a corrector signal C cancelling the error due to roll bending, if themill comprises means for detecting this bending. Thus, a signal epcorresponding to the actual rolling effort is obtained in wire 13. Thissignal ep is compared at 28 with the reference signal ef existing andthe difference is applied to wire 11, in a correcting amplifier 14. Thelatter delivers an output signal e3 which, as already explainedhereinabove, constitutes a reference signal for regulating the positionof plunger 5.

It is clear that this regulating circuit is adapted to constantly keepthe rolling effort, except for extremely short transitory time periods,at a value equal to a reference value represented by said signal ef.

The function of this first regulating circuit is to reduce to zero thevariations in thickness of the rolled product which are caused byvariations in the clamping pressure as a consequence of the out-of-trueof one or more rolls in the stand. Under these conditions it is obviousthat a clamping device having a high degree of dynamic performance mustbe used for the frequency of the correcting movements is relativelyhigh, i.e., of the order of several Hertz as far as the fundamentalcomponent is concerned.

However, so far as described this circuit cannot correct any defects dueto irregularities in the product itself. Therefore, the amplitude of themovements controlled by the clamping effort corrector is kept within thelimits of a certain range.

To this end, according to this invention, the signal e3 is also fed to acomparator 15 receiving on the other hand a reference signal emtransmitted via a wire 16. A signal corresponding to the difference (eme3) is delivered to the input terminal of a threshold device 17. Thisdevice is adapted to deliver a zero signal when the difference eme3 isless in absolute value than a certain constant K, and a signalproportional in absolute value to the quantity I em e3 I K, and of thesame sign as (em e3) when (em-e3) is greater in absolute value than K.The constant K is adjustable; its value must correspond exactly to thepeak-to-peak amplitude of the out-of-true.

An exemplary form of an embodiment of this aspect of the invention isshown diagrammatically in the FIG- URE.

The output signal of the threshold device 17 is fed to an integrator 18whose output signal is the ef signal corresponding to the referencevalue of the rolling effort.

The function of this second circuit may be described as follows: as longas the characteristics of the product remain nearly constant, therolling effort necessary for obtaining the final thickness also remainsconstant, and this value is memorized by the integrator 18.

The effort regulating circuit produces movements of the plunger 5 andtherefore of piston 6 for compensating very exactly the variations inthe clamping efforts which are caused by the out-of-true. The amplitudeof these movements is such that the reference signal e3 varies exactlywithin the above-defined range em: K. Thus, the threshold device 17delivers a zero signal and the output voltage of integrator 18 remainsconstant.

Now let us assume that the thickness of the incoming product increases.This will tend to increase the rolling effort by an amount ep. Theeffort regulating means react accordingly by causing a reduction in theclamping reference value e3; under these conditions, this value e3 willfall below the limit of the range emi K. Obviously, this will increasethe signal ef and therefore e3 until the latter signal e3 is returned tothe abovementioned range.

As it is, this arrangement will cancel the out-of-true effect whilemaintaining the natural rigidity of the rolling mill with respect to theirregularities of the product being processed therein. The defects dueto this lastmentioned cause are corrected by a third circuit accordingto the present invention.

To this end, the reference signal cf of the rolling effort is not onlyfed to the effort corrector but also to one input of comparator 19. Theother input of this comparator receives at 23 a reference voltage eocorresponding to a given, constant effort F0. The difference (ef eo) isamplified k times by an amplifier 20 whose output is fed to.an adder 21.This adder is an optional component of the third circuit and if providedit receives various correcting signals whose functions will be explainedpresently. The output of this adder is the reference signal em of thesecond circuit which limits the amplitude of the action exerted by theeffort corrector.

This third circuit operates as follows: when the characteristics of theproduct vary, and assuming for example that the input thicknessincreases, as explained in the foregoing, the clamping reference e3tends to overstep the limits of the range em i K imposed thereto, andthis is attended by an increase in the reference effort value ef. Moreexactly, in the selected example concerning an increase in the inputthickness e3 decreases and tends to become lower than em K.

As a consequence of the increase of ef, the third circuit describedhereinabove will cause em to increase, thus further increasing thequantity (em e3) K and also the reference value ef.

This second increase of ef is attended bya clamping effect since e3 mustincrease in order to maintain the quantity em e3 at least equal to K.

It can be seen that this third circuit operates somewhat like awell-known thickness regulator. These devices operate by compensating.the yield in proportion to the effort or to the effort variation. Moreparticularly, if the coefficient of amplification k2 of amplifier 20 isequal (with due consideration for the sensitivity of the position andpressure detectors) to the coefficient of elasticity kl of the rollingmill, it will be proved that the yield compensation is complete and theoutput thickness constant.

Therefore, these three circuits operatively linked in the mannerdescribed hereinabove impart to the rolling mill:

an infinite flexibility, within a certain range of adjustable amplitude.If care is taken to adjust this range within limits corresponding to thepeak-to-peak amplitude of the out-of-true, the latter becomesinoperative as far as the thickness of the product is concerned, aninfinite rigidity outside said range, so that the out-put thickness isindependent of variations in the characteristics of the incomingproduct.

It may also be noted that both the adjustment of constant K and that ofcoefficient k2, as well as the yield compensation, depend only on therolling mill, not on the rolled product.

Now the manner in which this arrangement is particularly adapted formaking secondary corrections, such as those likely to be derived frominformation supplied by thickness gauges disposed on the incoming and/oroutgoing product, will be described in detail.

Anticipated correction:

A thickness gauge may be disposed upstream of the rolling mill so as todetect any variation in thickness of the incoming product before it isengaged between the rolls. In this case it is extremely difficult toutilize this information, even with a suitable time-lag for takingaccount of the travel time betweenthe gauge and the roll stand, and atthe same time the system for compensating the yield proportional to theeffort variation. In fact, in this case two independent regulatingcircuits are involved and the correction orders issuing therefrom areadded to each other instead of substituting the order of the secondcircuit for that of the first.

However. it is perfectly possible to obtain this substitution by feedingvia a terminal 24 to the input 22 of integrator 18, through the mediumof a differentiation capacitor, the error signal delivered by theupstream thickness gauge. This may cause, for example, an increase inef. Now let us assume that the gain of this correction is so adjustedthat the increase in the reference value ef corresponds to the increasein the rolling effort to be created, by increasing the clamping force,for maintaining the output thickness constant. In this case:

the increase in the clamping force must be: k1 A F, where A F denotesthe increase in the rolling effort, and k1 is the coefficient ofelasticity of the rolling mill, as explained hereinabove.

except for the sensitivity of the pressure and position detector, thereference value em increases by the same quantity k1 A F since it wasadjusted as explained in the foregoing k2 Id, (k2 being the coefficientof amplification of 20, as already mentioned hereinabove).

therefore, since the variation of e3 was simultaneous with an equalvariation of em, the charge of integrator 18 is not modified.

If on the contrary the correction gain is inaccurate it will be seenthat when clearing one of the end or utmost points of the out-of-truethe charge of this integrator will be corrected, as a consequence of thepresence of the third circuit defined hereinabove.

In other words, the correction by upstream measurement provides apre-adjustment of the clamping force, which is subsequently and possiblymodified by the yield compensation chain.

Other secondary corrections can be applied to the regulation through themedium of adder 21, so as to cause a shift of the above-mentioned range.Therefore, the clamping-action modification will take place only when,as a consequence of the out-of-true, the quantity (em e3) has attainedits limit value K. Therefore, when an immediate correction is desired,there will be fed at the same time, to point 22 via a differentiationcircuit, a signal of such amplitude that it will produce substantiallythe effort variation corresponding to the signal fed to 21. It should benoted that in all cases the amplitude of the signal thus fed to 21 mustcorrespond to the variation in thickness which it is desired to obtainat the output, and not to a variation in the clamping effort which isnecessary to this end. In fact, the third yield compensation circuitadds its action to that of the signal fed to 21 so that the outputthickness variation will correspond to the amplitude of this signal.

As a consequence, it is possible to feed to 21 and 22 a correctionsignal obtained from information supplied by a thickness gauge locateddownstream of the rolling mm. It is also possible to introduce at thesepoint any necessary manual corrections. These inputs are showndiagrammatically in the form of a terminal 25.

Eventually, it will also be possible to introduce (but only into adder21) the signal for correcting the thickness variation resulting fromoil-film bearing play, or

any other correction of which an immediate application is not strictlynecessary (through inputs shown diagrammatically in the form of aterminal 26).

In the above description it is obvious that certain technologicalchoices have been made for illustrating the method and device of thepresent invention. However, it will readily occur to those skilled inthe art that these choices should not be construed as limiting the scopeof the invention. Thus, more particularly, numerical techniques may besubstituted for the analogical solutions described.

On the other hand, the results and modes of opera tion describedqualitatively can be justified mathematically and given quantitatively.More particularly, the stability of the various circuits has been provedand described. Therefore, these mathematical developments, which wouldonly burden unduly the specification without appreciably improving theunderstanding thereof, are omitted herein.

What I claim is:

1. In a rolling mill having a position-corrected under load clampingsystem, a means for accurately regulating the thickness of the rolledproduct, comprising:

a. means to measure the rolling effort of the rolling mill;

b. a primary correcting circuit connected to said measuring means andadapted to set the value of a clamping position correction in such amanner that the measured rolling effort is constantly very substantially equal to a first reference magnitude called an effortreference value;

c. a second correcting circuit connected to said first circuit and tosaid measuring means and adapted to determine the magnitude of the saideffort refer ence value, said second circuit comprising:

a dead zone device having the property of transmitting, in magnitude andsign, of the signal applied to the input of this device, only thefraction lying outside of a predetermined range, the limits of thisrange being disposed symmetrically on either side of a predeterminedmagnitude called a position reference,

a device having integrating and memory functions responsive to said deadzone device in such a manner that its output signal is the integral ofthe signal delivered by said dead zone device, this output signalconstitutes the effort reference value and is connected to a referenceinlet of said primary circuit; and

d. means for adjusting the width of the dead zone.

2. A device for controlling the thickness of a rolled product accordingto claim 1 wherein the position reference is determined by a thirdcircuit comprising a multiplying device for multiplying the effortreference magnitude, the coefficient of said multiplying device issubstantially equal to the coefficient of elasticity or yield of therolling mill and the output magnitude of said multiplying device is fedto a position reference input of said dead zone device.

3. A device for regulating the thickness of a rolled product accordingto claim 2 further including a thickness gauge located near the input tosaid rolling mill for measuring the thickness of the product fed to saidmill; said gauge having an output connected to the input of said devicehaving integrating and memory functions.

4. A device for regulating the thickness of a rolled product accordingto claim 3 further including a second thickness gauge for measuring thethickness of the product emerging from the mill; said second gaugehaving an output also connected to the input of said device havingintegrating and memory functions, the output of said second gaugefurther being added to the output of said multiplying device of saidthird circuit.

5. A device for regulating the thickness of :1 rolled product accordingto claim 3 further including a time delay device connected between theoutput of said gauge and the input of said device having integrating andmemory functions for delaying the signal fed to said input a time equalto the time needed for the measured product to reach the mill.

6. A device for regulating the thickness of a rolled product accordingto claim 1 further including a thickmagnitude of the dead zone device.

1. In a rolling mill having a position-corrected under load clampingsystem, a means for accurately regulating the thickness of the rolledproduct, comprising: a. means to measure the rolling effort of therolling mill; b. a primary correcting circuit connected to saidmeasuring means and adapted to set the value of a clamping positioncorrection in such a manner that the measured rolling effort isconstantly very substaNtially equal to a first reference magnitudecalled an effort reference value; c. a second correcting circuitconnected to said first circuit and to said measuring means and adaptedto determine the magnitude of the said effort reference value, saidsecond circuit comprising: a dead zone device having the property oftransmitting, in magnitude and sign, of the signal applied to the inputof this device, only the fraction lying outside of a predeterminedrange, the limits of this range being disposed symmetrically on eitherside of a predetermined magnitude called a position reference, a devicehaving integrating and memory functions responsive to said dead zonedevice in such a manner that its output signal is the integral of thesignal delivered by said dead zone device, this output signalconstitutes the effort reference value and is connected to a referenceinlet of said primary circuit; and d. means for adjusting the width ofthe dead zone.
 2. A device for controlling the thickness of a rolledproduct according to claim 1 wherein the position reference isdetermined by a third circuit comprising a multiplying device formultiplying the effort reference magnitude, the coefficient of saidmultiplying device is substantially equal to the coefficient ofelasticity or yield of the rolling mill and the output magnitude of saidmultiplying device is fed to a position reference input of said deadzone device.
 3. A device for regulating the thickness of a rolledproduct according to claim 2 further including a thickness gauge locatednear the input to said rolling mill for measuring the thickness of theproduct fed to said mill; said gauge having an output connected to theinput of said device having integrating and memory functions.
 4. Adevice for regulating the thickness of a rolled product according toclaim 3 further including a second thickness gauge for measuring thethickness of the product emerging from the mill; said second gaugehaving an output also connected to the input of said device havingintegrating and memory functions, the output of said second gaugefurther being added to the output of said multiplying device of saidthird circuit.
 5. A device for regulating the thickness of a rolledproduct according to claim 3 further including a time delay deviceconnected between the output of said gauge and the input of said devicehaving integrating and memory functions for delaying the signal fed tosaid input a time equal to the time needed for the measured product toreach the mill.
 6. A device for regulating the thickness of a rolledproduct according to claim 1 further including a thickness gauge formeasuring the thickness of the product emerging from the mill; theoutput of said gauge being connected to the input of said integratingand memory device and also being added to the position referencemagnitude of the dead zone device.
 7. A device for regulating thethickness of a rolled product according to claim 2 further including athickness gauge for measuring the thickness of the product emerging fromthe mill; the output of said gauge being connected to the input of saidintegrating and memory device and also being added to the positionreference magnitude of the dead zone device.